1. Technical Field
The present invention relates to a fuel injection valve that injects a fuel by opening and closing a needle valve.
2. Background Art
FIG. 12 is a sectional view showing a conventional fuel injection valve disclosed in the Japanese Patent Publication (unexamined) No. 47208/1998. In this fuel injection valve, a swirler 22 is disposed upstream an injection port 21, and a valve element 23 has a conical end portion.
The valve is operated as described below. When applying an electric current to a coil 24, an armature 25 is attracted toward a core 26, the needle valve 23 integrally formed with the armature 25 separates from a valve seat 27, and a fuel is injected from a gap between the valve seat 27 and the needle valve 23.
When interrupting the application of electric current to the coil 24, the needle valve 23 is pushed toward the valve seat 27 by a spring 28, and the needle valve 23 comes in contact with the valve seat 27. Opening and closing this needle valve 23 control the amount of fuel to be injected.
Another conventional example is disclosed in the Japanese Patent Publication (unexamined) No. 113163/1993. In this prior art, the valve seat of the fuel injection valve is arranged to have a convex configuration continuously protruding toward the passage, the valve element has a conical end portion, and volume of the passage below the valve element is arranged not to be larger than that in the vicinity of a seat portion (a portion where the valve element comes in contact with the valve seat when the valve is closed) in order to prevent turbulence such as vortex.
The flow of the fuel is accelerated in order to prevent turbulence by continuously reducing the passage area from the seat portion to the injection port.
Since the conventional fuel injection valves has been constructed as described above, the fuel injection valve disclosed in Japanese Patent Publication (unexamined) No. 47208/1998 has a problem that carbon produced in the engine combustion chamber comes to stick onto inner wall face of the injection port 21 of the fuel injection valve and onto the face of the valve seat 27 as shown in FIG. 13. This causes lowering in flow rate and change in spray angle.
Particularly on the valve seat 27 facing immediately downstream a seat portion C, carbon deposit W sticks considerably to a portion D where the swirling force is not sufficiently amplified. This portion is smaller than the injection port 21 in sectional area of the passage, and therefore the carbon sticking brings about a serious influence of reduction in flow rate.
FIG. 14 is a graph showing the relation between several points from a swirl-generating portion A to a downstream point F and flow velocity of swirl.
Next, in the case that the fuel injection valve is constructed as disclosed in the Japanese Patent Publication (unexamined) No. 113163/1993, function of the accelerated flow of the fuel, i.e., fuel flow at a high speed is advantageous in the aspect of effectively washing out the carbon in the area from the seat portion to the injection port. Accordingly, there is a possibility that the problem incidental to the Japanese Patent Publication (unexamined) No. 47208/1998 be solved by such construction as disclosed in the Japanese Patent Publication (unexamined) No. 113163/1993.
Generally in the fuel injection valve provided with a fuel swirl generating portion upstream the injection port, it is desirable that the flow rate at the time of fully opening the valve is decided depending upon the swirling force generated at the swirl generating portion and the inner diameter of the injection port. However, when the sectional area of passage is established to be not larger than a predetermined value in the seat portion between the swirl generating portion and the injection port or in the portion downstream thereof, the flow rate at the time of fully opening the valve is reduced, the swirling force is also decreased, and the injected fuel is not satisfactorily turned into minute particles.
Therefore, it is necessary that sectional area of the passage in the seat portion and the portion downstream the seat portion is established to be larger than a predetermined value. But when the sectional area of passage in the seat portion is excessively large, stroke of the valve element becomes large and response characteristic is deteriorated.
However, when forming the sectional area of passage in the portion downstream the seat portion to be smaller than that of the seat portion as is done in the fuel injection valve proposed by the Japanese Patent Publication (unexamined) No. 113163/1993, the inlet portion of the injection port has the minimum sectional area of passage. The sectional area of passage in the inlet portion of the injection port is decided depending upon configuration of the portion connecting the valve seat face and the injection port, configuration of the valve element, and stroke of the valve element. Hence, it is difficult to control the sectional area of passage with a small tolerance in mass production.
Likewise, it is also difficult to control a passage sectional area of the seat portion, which is larger than that in the inlet portion of the injection port, with a small tolerance. As a result, the passage sectional area of the seat portion is arranged so large as to have a certain clearance, and such a construction is not free from deterioration in response characteristic.
The present invention was made to resolve the above-discussed problems and has an object of reducing carbon deposit sticking to the passage portion downstream the seat portion between the seat portion and the injection port without deterioration in response characteristic.
A fuel injection valve according to claim 1 of the invention comprises: a hollow valve holder, a valve seat portion mounted on an end of the valve holder and provided with an injection port, a valve element for opening and closing the injection port by moving in the valve holder to come in contact with and separate from the valve seat portion, and a swirler disposed surrounding the valve element to slidably support the valve element and swirling a fuel flowing out of the injection port;
wherein a part of valve seat face downstream a seat portion, where the valve element comes in contact with the valve seat to interrupt fuel injection, is formed into a tapered face.
As a result, it is possible to reduce carbon deposit sticking to the passage portion.
In the fuel injection valve according to claim 2 of the invention, diameter of a starting point upstream the tapered face is established to be not more than 1/2.5 of an inner diameter of a swirl chamber of the swirler.
As a result, lowering in flow rate at the time of fully opening the valve can be restricted to an allowable value or less.
In the fuel injection valve according to claim 3 of the invention, a step portion is formed at a part where the tapered face and the valve seat face join together.
As a result, it is possible to improve function of shearing carbon deposit.
In the fuel injection valve according to claim 4 of the invention, the injection port is arranged to be inclined with respect to a center axis of the valve.
As a result, it is possible to ease uneven fuel flow in the injection port.